The present invention relates to electroencephalographs and more particularly to accessory devices to be used in conjunction with an electroencephalograph to provide system parameter data to an operator thereof.
In a standard electroencephalograph (EEG) system, a plurality of electrodes are attached to a patient's scalp according to a given, well established, pattern. The signals emanating from the brain are detected by these electrodes and conducted to the EEG instrument where they are amplified and made available for display on a multiple pen recorder. The EEG instrument typically has a number of parameters which can be set by the operator to determine the amplification factors and display sequence on the recorder of the signals being sensed. For example, the electrodes can be assigned to particular channels, the gain of the individual channel amplifiers adjusted, and various filters and time constants inserted and set to exclude extraneous electrical impulses being sensed by the electrodes from such sources as electric lights, other equipment, etc. Also, the data gathered must be identified with the particular patient. Additionally, certain patterns associated with the electrodes chosen to be sampled and the placement of their signal on the recorded output are standard and, therefore, "preset" in many EEG instruments. That is, the operator merely sets a configuration number on a preset selection dial to cause a particular set of electrodes to be assigned to previously selected channels.
Since the interpretation of the recorded output is dependent upon all these input parameters, the operator must physically mark the parameter data upon the recorded output when it is changed. This, of course, is a time consuming task which is prone to error production through the mismarking of data or through inexact handwriting which is misread at a later date.
Attempts have been made by others to provide system parameter data to the operator through the recorded output. In one system, a pulse coding of spikes is provided on a dedicated event marker channel in response to specific inputs by the operator on a pushbutton keyboard. Such a system is, of course, not automatic and the output must be interpreted as to meaning. In yet another system, two back-to-back pens are dedicated and positioned so as to print actual letters and numerals. Such an approach can automatically provide limited information in a readable form but leaves much necessary data undisplayed. Further, an extra recording channel must be utilized in addition to the one usually provided for "event" marking. Moreover, a minor malfunction in the operation of one or both of the pens can result in an output which can vary from difficult to comprehend to completely unreadable.
Thus, it is an object of the present invention to provide an EEG instrument providing means for automatically including the aforementioned parameter data on the recorded output of the EEG in a simple manner which is instantly and constantly recognizable by the operator at a later time.